Differences in Cellular Encapsulation of Six Termite (Isoptera) Species Against Infection by the Entomopathogenic Fungus Metarhizium anisopliae

Thomas Chouvenc, Nan-Yao Su, Alain Robert

Abstract

Termites (Isoptera) are eusocial insects, which live in an environment that can favor the spread of pathogens. To reduce the chance of an epizootic within a colony, termites have evolved many defense mechanisms. Most studies have focused on the social aspect of disease resistance, while the individual capacity of a termite to survive an infection remains poorly documented. We previously showed that when the eastern subterranean termite, Reticulitermes flavipes (Kollar), was exposed to the entomopathogenic fungus, Metarhizium anisopliae (Metch.) Sorokin, cellular encapsulation of the penetrating fungus was one of the last lines of defense for individual termites to prevent internal mycosis. The current study used histological preparations to (i) compare cellular encapsulation of M. anisopliae among 6 termite species from 5 families that evolved in habitats with different pathogenic pressures, and (ii) examine the effect of cellular encapsulation on the survival of termites exposed to M. anisopliae. Our results showed that all termite species were able to use hemocytes to encapsulate M. anisopliae when this fungus penetrated through the insect cuticle, but that the physiological cost to successfully encapsulate M. anisopliae varied greatly among termite species. We suggest that termite species, which evolved in a habitat with high pathogenic pressure, are adapted with more efficient immune reactions than those that evolved in a habitat with low pathogenic pressure.